Method of selectively removing metal nitride or metal oxynitride extrusions from a semmiconductor structure

ABSTRACT

Metal nitride and metal oxynitride extrusions often form on metal silicides. These extrusions can cause short circuits and degrade processing yields. The present invention discloses a method of selectively removing such extrusions. In one embodiment, a novel wet etch comprising an oxidizing agent and a chelating agent selectively removes the extrusions from a wordline in a memory array. In another embodiment, the wet etch includes a base that adjusts the pH of the etch to selectively remove certain extrusions relative to other substances in the wordline. Accordingly, new metal silicide structures can be used to form novel wordlines and other types of integrated circuits.

This application is a continuation of U.S. application Ser. No.10/234,577, filed on Aug. 30, 2002, which is a continuation of U.S.patent application Ser. No. 09/738,796, filed on Dec. 15, 2000, which isnow U.S. Pat. No. 6,455,906, which is a divisional of U.S. patentapplication Ser. No. 09/385,396, filed Aug. 30, 1999, which is now U.S.Pat. No. 6,358,788, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the removal of extrusions that formduring the fabrication of integrated circuits. More particularly, theinvention relates to the removal of extrusions that form onmetal-oxide-semiconductor (MOS) structures.

2. Description of the Related Art

In order to improve speed and performance in semiconductor components,manufacturers typically attempt to decrease access time of varioussemiconductor structures located in the components by incorporatinglayers of materials which enhance electron flow into semiconductorstructures. For example, to increase read/write speed in memory cells,such as dynamic random access memory (DRAM), semiconductor manufacturersattempt to decrease wordline access time by reducing the resistance orcapacitance in a wordline. Reduction of resistance is typically achievedby layering a low-resistance conductive material over the gate in asemiconductor structure.

Some manufacturers use materials such as titanium silicide (TiSi_(x)),known for its low resistance, to form the conductive layer of asemiconductor structure. Titanium silicide, however, can become unstableduring subsequent high temperature processing steps and can diffuse intothe underlying gate layer (typically polysilicon), also called titaniumsilicide agglomeration, thereby damaging the semiconductor structure. Toprevent titanium silicide agglomeration, some manufacturers cover thegate layer with a barrier layer, such as titanium nitride (TiN).Depending on the thickness of the barrier layer, however, the titaniumnitride may possess a high resistance and thus detract from the lowresistance effect of the conductive layer. Furthermore, duringsubsequent processing at high temperature and an oxygen atmosphere,titanium nitride can oxidize to form titanium oxynitride (TiO_(x)N_(y)).

Likewise, during subsequent processing, semiconductor structurescontaining metal silicide layers that may be exposed to nitrogen andoxygen rich environments at high temperature. These gases react withmetal rich portions of the semiconductor structure to create metaloxynitrides. Such metal oxynitrides may expand to create extrusionswhich protrude outwardly from the sides of the semiconductor structure.If these extrusions contact other portions of the semiconductor, shortcircuits result.

To reduce the probability of short circuits resulting from extrusions,some manufacturers coat the semiconductor structure with an insulatorsuch as a nitride spacer. While these coatings reduce the amount andextent of extrusions formed, application of such coatings is a complexand expensive process. Furthermore, these coatings may interfere withfurther processing steps thereby increasing manufacturing costs anddecreasing semiconductor component yields.

SUMMARY OF THE INVENTION

A conductor, preferably composed of a tungsten silicide (WSi_(x))barrier layer and a titanium silicide (TiSi_(x)) conductive layer, isdisclosed for use in a semiconductor structure such as a wordline,transistor or any other structure. A novel wet etch, preferably composedof an oxidizing and chelating agent in solution, is further disclosedfor selectively removing extrusions which may protrude from theconductor.

Exemplary methods of creating the conductor include sputtering tungstensilicide onto a polysilicon gate to create a tungsten silicide layer.Titanium silicide is then sputtered onto the tungsten silicide layer.Exemplary formulations of the wet etch include a combination of anoxidizing agent such as hydrogen peroxide (H₂O₂) in water with aquantity of a chelating agent such as ethylenediaminetetraacetic acid(EDTA). In other embodiments, the wet etch comprises water, an oxidizingagent, a chelating agent and a base such as ammonium hydroxide. In yetother embodiments, the wet etch comprises water, an oxidizing agent, achelating agent, a base and a buffer salt such as ammonium phosphate.

One aspect of the invention relates to a method of fabricating awordline in a memory array. The method comprises depositing a tungstensilicide barrier layer on a wordline stack and processing the wordlinestack such that tungsten nitride extrusions extend from an exposedsurface of the barrier layer. The method further comprises selectivelyetching the tungsten nitride extrusions with a solution that compriseswater, hydrogen peroxide and EDTA.

Another aspect of the invention relates to a method of fabricating awordline in a memory array. The method comprises depositing a metalsilicide layer on a wordline stack and processing the wordline stacksuch that metal nitride extrusions extend from the metal silicide layer.The method further comprises selectively etching the metal nitrideextrusions with a solution that comprises at least an oxidizing agentand a chelating agent.

An additional aspect of the invention relates to a method of fabricatinga wordline in a memory array. The method comprises depositing a tungstensilicide barrier layer on a wordline stack and depositing a titaniumsilicide conductive layer above the tungsten silicide barrier layer. Themethod further comprises processing the wordline stack such that metalnitride extrusions extend from the tungsten silicide barrier layer andthe titanium silicide conductive layer. The method also comprisesetching the metal nitride extrusions at a faster rate than theconductive layer or the barrier layer.

One embodiment of the invention relates to a method of fabricating asemiconductor structure. The method comprises depositing a polysilicongate on a semiconductor substrate to form a wordline stack anddepositing a conductive layer comprising metal silicide above thepolysilicon gate. The method further comprises processing the wordlinestack in a manner that forms protrusions on the conductive layer andetching the protrusions at a faster rate than the conductive layer.

Another embodiment of the invention relates to a method of forming awordline gate that comprises forming metal nitride extrusions on awordline stack and selectively removing the metal nitride extrusions. Anadditional embodiment relates to a method of forming a semiconductorstructure. The method comprises selectively removing metal oxynitrideextrusions from a semiconductor structure in a manner that does notsubstantially damage a conductive layer in the semiconductor structure.

Yet another embodiment relates to a method of removing metal oxynitrideextrusions from a semiconductor structure in a manner that does notsubstantially damage a polysilicon layer in the semiconductor structure.A further embodiment relates to a method of forming a wordline gate. Themethod comprises forming metal oxynitride extrusions on a wordline stackand selectively removing the metal oxynitride extrusions.

One aspect of the invention relates to a wet etch for selectivelyremoving tungsten nitride extrusions that comprises at least 10% byweight hydrogen peroxide and at least 0.03% by weight EDTA. Anotheraspect of the invention relates to a wet etch for selectively removingmetal nitride extrusions that comprises at least 10% by weight an and atleast 0.03% by weight a chelating agent.

One embodiment of the invention relates to a semiconductor structurethat comprises a tungsten silicide layer, wherein the tungsten silicidelayer has substantially etched tungsten nitride extrusions formedthereon. Another embodiment relates to a semiconductor structure thatcomprises a tungsten silicide layer, wherein the tungsten silicide layerhas substantially etched tungsten oxynitride extrusions thereon. Anadditional embodiment relates to a semiconductor structure thatcomprises a titanium silicide layer, wherein the titanium silicide layerhas substantially etched titanium nitride extrusions thereon. Yetanother embodiment relates to a semiconductor structure that comprises atitanium silicide layer, wherein the titanium silicide layer hassubstantially etched titanium oxynitride extrusions thereon.

Another aspect of the invention relates to a semiconductor structurethat comprises a barrier layer above a semiconductor substrate, thebarrier layer comprising a tungsten silicide. The semiconductorstructure further comprises a conductive layer above the wordline gate,the conductive layer comprising titanium silicide. The semiconductorstructure also comprises a cap above the conductive layer.

For purposes of summarizing the invention, certain aspects, advantagesand novel features of the invention are described herein. It is to beunderstood that not necessarily all such advantages may be achieved inaccordance with any particular embodiment of the invention. Thus, forexample, those skilled in the art will recognize that the invention maybe embodied or carried out in a manner that achieves one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, advantages, and novel features of the inventionwill become apparent upon reading the following detailed description andupon reference to the accompanying drawings.

FIG. 1 is a diagram depicting communication between a microprocessor anda memory device.

FIG. 2 shows a memory array containing multiple wordlines and bitlines.

FIG. 3 is a cross-sectional view of a wordline in accordance with oneembodiment of the invention.

FIG. 4 shows a top view of wordline stacks in a memory array.

FIG. 5 is a top angled view of a wordline stack after source/drainreoxidation and before wet cleaning.

FIG. 6 is a top angled view of a wordline stack after wet cleaning.

FIG. 7 is a processing flow diagram illustrating the processing blocksfor one embodiment of wordline stack fabrication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A conductor, preferably composed of a tungsten silicide (WSi_(x))barrier layer and a titanium silicide (TiSi_(x)) conductive layer, isdisclosed for use in a semiconductor structure such as a wordline,transistor or any other structure. A wet etch, preferably composed of anoxidizing and chelating agent in solution, is further disclosed forremoving extrusions which may protrude from these low-resistancesegments.

As illustrated in FIG. 1, a novel memory array 10 is disclosed hereinthat interfaces with other electronic circuitry 12 via conventionaladdress signals 14 and data signals 16. The address signals 14 selectone or more memory cells in the memory array 10. The data signals 16, onthe other hand, carry data that is stored in or retrieved from thememory array 10.

In one embodiment, the memory array 10 disclosed herein is a synchronousdynamic random access memory (SDRAM). In other embodiments the memoryarray 10 may comprise a wide variety of memory devices such as staticmemory, dynamic memory, extended data out memory or any other memorytype known in the art.

The memory array 10 interfaces with different types of electroniccircuitry 12. By way of example, the electronic circuitry 12 can includeany device, which accesses or relies on memory including, but notlimited to, processors, controllers, and the like. In some embodiments,the memory array 10 and the electronic circuitry 12 are implementedseparately, in other embodiments the memory array 10 and the electroniccircuitry 12 are integrated together. Furthermore, one of ordinary skillin the art will recognize that the memory array 10 can be implemented ina wide variety of devices, products and systems.

FIG. 2 illustrates a memory array 10 that comprises a plurality ofmemory cells 20. These memory cells 20 are organized into columns C_(N)and rows R_(N). A column decoder 24 and a row decoder 26 process theaddress signals 14 to identify the column C_(N) and row R_(N) of thetargeted memory cells 20. The columns are commonly known as bitlines andthe rows are typically known as wordlines to those skilled in the art.

FIG. 3 illustrates a cross-sectional view of a wordline R_(N) and FIG. 7illustrates an associated method for making one embodiment of thewordline R_(N). In one embodiment, a semiconductor substrate 30, formedin a processing block 154, comprises two field oxide regions, 32 and 34.The semiconductor substrate 30 may include semiconductor structuresand/or other layers that have been fabricated thereon in a processingblock 158 or any doped silicon platform that is commonly used in theart. While the illustrated semiconductor substrate 30 comprises anintrinsically doped monocrystalline silicon wafer, it will be understoodby one of skill in the art of semiconductor fabrication that thesemiconductor substrate 30 in other arrangements can comprise otherforms of semiconductor layers which include active or operable portionsof semiconductor devices.

The semiconductor substrate 30 is further processed in processing block162 to create a gate comprising two n+ regions using methods common tothose of skill in the art. The first n+ region 40 acts as a source andthe second n+ region 42 acts as a drain. Hereinafter the first n+ region40 will be referred to as the source 40 and the second n+ region 42 willbe referred to as the drain 42. Each wordline R_(N) further comprises aplurality of layers, which will herein be called a wordline stack 50.The layers in the wordline stack 50 comprises a dielectric layer 60, apolysilicon layer 70, a conductive segment 80 and a cap 90.

In one embodiment, the dielectric layer 60 is a gate oxide comprisingsilicon dioxide (SiO₂). The dielectric layer 60 is applied by wet or dryoxidation of the semiconductor substrate 30 followed by etching througha mask, or by other techniques common to those of skill in the art. Inone embodiment, the dielectric layer 60 is approximately 60-90 angstroms(Å) thick. The polysilicon layer 70, in one embodiment, may be depositedonto the dielectric layer 60 through chemical vapor in the art. In oneembodiment, the polysilicon layer 70 is approximately 1,000 Å thick.

The conductive segment 80 interconnects the source 40 and drain 42. Inone embodiment, the conductive segment 80 comprises a conductive layer100 and an optional barrier layer 102. The conductive layer 100 istypically a metal layer that forms a metal-poly gate. The conductivelayer 100, when implemented over the polysilicon layer 70, lowers theoverall resistivity of the wordlines R_(N) while retaining the gateintegrity provided by the polysilicon layer 70. Typically, theconductive layer 100 comprises a layer of metal silicide. One of thefunctions of the conductive layer 100 is to carry the charge to thememory cells 20 in communication with a wordline R_(N).

In one embodiment, the conductive layer 100 is comprised of titaniumsilicide (TiSi_(x)) which is deposited in a processing block 170 byphysical vapor deposition in an Argon environment. Suitable sputteringreactors are commercially available from Applied Materials of SantaClara, Calif. In one embodiment, argon gas is introduced into thesputtering chamber at a rate of between about 50 standard cubiccentimeters per minute (sccm) and 100 sccm for approximately 8 to 10seconds. The DC magnetron power of the preferred sputtering reactor isgenerally set at approximately 1.0 kilowatts (kW) to approximately 2.0kW, preferably at approximately 1.5 kW. In light of the presentdisclosure, however, the skilled artisan can readily determine theappropriate sputtering parameters through routine optimization toachieve the desired titanium silicide composition in a given reactorconfiguration.

In this embodiment the conductive layer 100 is approximately 1,000 Åthick and has a resistivity of approximately 15-20 μΩ-cm. The conductivelayer 100 may also posses metal-rich pockets. For example, if theconductive layer 100 comprises titanium silicide, titanium-rich pocketsmay exist in the conductive layer 100.

Those of ordinary skill in the art will recognize that the conductivelayer 100 may also be made from a variety of metals. Additional examplesof suitable metals for forming the conductive layer 100 include, but arenot limited to, copper, gold, aluminum, silicon, cobalt silicide, nickelsilicide, and the like. Mixtures of metals are also suitable for formingthe conductive layer 100. Exemplary methods of depositing the conductivelayer 100 include, but are not limited to, Rapid Thermal Chemical VaporDeposition (RTCVD), Low Pressure Chemical Vapor Deposition (LPCVD), andPhysical Vapor Deposition (PVD).

When the memory array 10 is subjected to further processing, portions ofthe conductive layer 100 may diffuse into the polysilicon layer 70,thereby damaging the polysilicon layer 70. For example, if theconductive layer 100 comprises titanium silicide, the stability of thetitanium silicide decreases when the semiconductor structure is exposedto temperatures exceeding 850° C. during further processing. Thus,absent a barrier layer 102, the titanium silicide tends to diffuse intothe polysilicon layer 70 thereby degrading the polysilicon.

In one embodiment, the barrier layer 102 exists between the conductivelayer 100 and the polysilicon layer 70. In other embodiments, thebarrier layer 102 may not exist. While the barrier layer 102electrically connects the conductive layer 100 and the polysilicon layer70, it also inhibits diffusion of impurities between those layers andprotects the polysilicon layer 70 during further processing as describedbelow. In one embodiment, the barrier layer 102 comprises a variety ofmetal silicides such as tungsten silicide (WSi_(x)) which is depositedin a processing block 166 by physical vapor deposition in an argonenvironment.

Suitable sputtering reactors are commercially available from AppliedMaterials of Santa Clara, Calif. In one embodiment, argon gas isintroduced into the sputtering chamber at a rate of between about 50standard cubic centimeters per minute (sccm) and 100 sccm forapproximately 5 to 10 seconds. The DC magnetron power of the preferredsputtering reactor is generally set at approximately 0.5 kilowatts (kW)to approximately 2.0 kW, preferably at approximately 1.0 kW. In oneembodiment, the applied tungsten silicon is approximately WSi_(2.7). Inaddition, the tungsten silicide remains stable up to temperatures ofapproximately 1050° C., thereby protecting the polysilicon layer 70during high temperature anneals and other high-temperature processing.

In this embodiment, the barrier layer 102 is approximately 150 Å thickand has a resistivity of approximately 60 μΩ-cm. The thinness of thebarrier layer 102 combined with the low resistance of tungsten silicideimproves gate access.

In light of the present disclosure, however, the skilled artisan canreadily determine the appropriate sputtering parameters through routineoptimization to achieve the desired barrier layer 102 composition in agiven reactor configuration. Furthermore, one of ordinary skill in theart will recognize that the thickness and resistivity of the barrierlayer 102 can vary over a range of values. Those of ordinary skill inthe art will also recognize that the barrier layer 102 can comprise avariety of materials such as titanium nitride, silicon nitride or othermaterials, which protect the polysilicon layer 70.

Local variations in the uniformity of the barrier layer 102 can createmetal-rich areas. These metal-rich areas may be due in part tostoichiometry variations due to the thinness of the barrier layer 102.For example, if the barrier layer 102 comprises tungsten silicide,tungsten-rich areas can exist within the tungsten silicide composition.The wordline stack 50 further comprises the cap 90, which is depositedin a processing block 174 onto the conductive segment 80 to protect theunderlying materials during further processing. In one embodiment, thecap 90 comprises a layer of silicon oxide (SiO₂) which is deposited ontothe conductive layer by chemical vapor deposition, or by othertechniques common to those of skill in the art. In another embodiment,the cap 90 further comprises a layer of silicon nitride (Si₃N₄) which isdeposited onto the silicon oxide layer by chemical vapor deposition, orby other techniques common to those of skill in the art. In yet anotherembodiment, the cap 90 comprises silicon nitride as the primarypassivating layer. Those of skill in the art will recognize that the cap90 may be made of various common insulating materials or theircombination.

The wordline stack 50 is further patterned through etching. FIG. 4illustrates a top view of several wordline stacks in one embodiment of amemory array 10. Each wordline stack 50 in this embodiment is “S”shaped. In the preferred embodiment, the etch comprises a level 50in-situ dry etch. The etch may also comprise other dry or wet etchescommon to those of skill in the art. The patterning stops at the gateoxide 60 or the substrate 30, and then the source 40 and the drain 42regions are formed. In one embodiment, the source 40 and the drain 42are doped with n-type dopants using techniques common to those of skillin the art.

After patterning the wordline stack 50, or in other processing steps,the wordline stack 50 is often exposed to nitrogen rich environments.The nitrogen may react with metal rich pockets in the conductive segment80. For example, in an embodiment where the barrier layer 102 comprisestungsten silicide with tungsten-rich pockets, the tungsten rich pocketsmay react with the nitrogen to form tungsten nitride (WN_(x)). In otherembodiments, where the conductive layer 100 comprises titanium silicidewith titanium-rich pockets, the titanium-rich pockets may also reactwith the nitrogen to form titanium nitride (TiN_(x)).

In addition, a source/drain reoxidation is applied in a processing block178 to partly fix dry etch damage and to improve device reliability.This reoxidation subjects the memory array 10 to an oxygen richenvironment. While the oxygen reoxidizes the areas existing near thesource and drain, the oxygen may also combine with the tungsten nitrideand titanium nitride areas existing in the conductive layer 100 and thebarrier layer 102 in various embodiments. When the oxygen reacts withthese layers, metal oxynitrides, such as tungsten oxynitride(WO_(x)N_(y)) and titanium oxynitride (TiO_(x)N_(y)) are formed. Stillfurther, titanium-rich and tungsten-rich areas may combine with nitrogenand then oxygen to form titanium tungsten oxynitrides (TiWO_(x)N_(y)).One of ordinary skill in the art will also recognize that in otherembodiments, other metals in the barrier or conductive layers cancombine with oxygen to create different types of metal oxynitrides.

As illustrated in FIG. 5, when the metal oxynitrides form, they expandrelative to the remainder of the other conductor materials. Thisexpansion can create extrusions 140 that extend outwardly from the sidesof the wordline stack 50. These extrusions 140 can contact otherportions of the memory array 10, thereby creating short circuits whichcan alter the operation of the memory array 10 or even render the memoryarray 10 unusable.

For example, in one embodiment where the conductive layer 100 comprisestitanium silicide and the barrier layer 102 comprises tungsten silicide,the extrusions 140 may comprise tungsten oxynitride, titaniumoxynitride, and/or titanium tungsten oxynitride. These extrusions 140not only extend outward from the exposed surface of the conductive layer100, but also extend outward from the exposed surface of the barrierlayer 102. While the dimensions of the extrusions 140 vary, the width istypically less than 10 nm and the length is approximately 30 nm toapproximately 50 nm.

As explained above, these extrusions 140 can cause shorts in the memoryarray 10. In one example, 360 memory arrays with a titanium silicideconductive layer 100 and a tungsten silicide barrier layer 102 wereconstructed on a single wafer. After the wafer was processed, only 10 ofthe 360 memory arrays operated properly.

Although the extrusions 140 have been described with respect to thebarrier layer 102 and conductive layer 100 of a wordline stack 50, itshould be understood that such extrusions 140 can develop in a widerange of devices which use metal-based conductors such as transistorsand the like. For example, the extrusions 140 can develop on a widevariety of metal silicides, which are then exposed to nitridizingconditions. Furthermore, the extrusions 140 can develop metal nitrides,which are exposed to oxidizing conditions.

The extrusions 140 can be removed in a processing block 182 by a uniquetechnique which allows for selective dissolution of the extrusions 140without significantly harming the materials of the wordline stack 50. Inone embodiment, a memory array 10 is subjected to a novel wet etch thatremoves the extrusions 140, as illustrated in FIG. 6. The novel wet etchcomprises an oxidizing agent and a chelating agent in solution.

In one embodiment, the oxidizing agent is hydrogen peroxide (H₂O₂).Preferably, the wet etch is approximately 10% by weight hydrogenperoxide. In other embodiments, the amount of hydrogen peroxide can varyfrom 2% to 50%. In further embodiments, the oxidizing agent can includeany of a variety of substances including, but not limited to, ozonatedwater, ozone, nitric acid (HNO3), hypochlorous acid (HClO), chloric acid(HClO₃), ammonium persulphate ((NH₄)₂S₂O₈), sulfuric acid (H₂SO₄), andthe like.

In one embodiment, the chelating agent is ethylenediaminetetraaceticacid (EDTA) that is approximately 0.03% by weight EDTA. In otherembodiments, the amount of EDTA in the wet etch can range fromapproximately less than 0.001% to more than 5% by weight EDTA. Infurther embodiments, the chelating agent can be any of a variety ofsubstances including, but not limited to, ligands, the amine group, thecarboxylic acid group compounds, oxalate, acetate, disodiumethylenediamine acid (H₂NC₂H₄NH₂), glycine (NH₂CH₂COOH), iminodiaceticacid (NH(CH₂COOH)O₂), nitrolotriacetic acid (N(CH₂COOH)₃), tetraammoniumethylenediaminetetraacetate, tetramethylammoniumethylenediaminetetraacetate, and the like.

In a further embodiment, the etch comprises a combination of anoxidizing and chelating agent and further comprises a base. The base maybe used to adjust the pH of the etch solution to improve cleaning andselectivity. In one embodiment, the base is ammonium hydroxide (NH₄OH).In another embodiment, the wet etch is approximately 0.02% ammoniumhydroxide, 0.042% EDTA and 10% hydrogen peroxide and has a pH of aboutseven to eight. In other embodiments, the amount of ammonium hydroxidecan vary over a wide range such as from approximately 0.5% toapproximately 30% by weight, depending on the desired pH. In furtherembodiments the base can be any of a variety of bases including, but notlimited to, tetramethyl ammonium hydroxide (TMAH), trimethoxyamphetamine(TMA), choline hydroxide, sodium hydroxide, potassium hydroxide, and thelike.

In still a further embodiment, the etch solution comprises a combinationof an oxidizing agent, a chelating agent, a base and a buffer salt. Thebuffer salt may be added to help maintain a constant pH level and toform a protective layer on the other materials of the stack to assistselectivity. In one embodiment, the buffer salt is potassium sulfate(K2SO4) that is approximately 2% potassium sulfate. In otherembodiments, the amount of potassium sulfate can vary over a wide range,depending on the pH and concentration of other substances in the wetetch solution. In further embodiments, the buffer salt can be any of avariety of salts including, but not limited to, potassium phosphate,diammonium phosphate, and the like.

In one embodiment, the wet etch is heated to 65° C. It has been foundthat a 65° C. wet etch comprising 10% hydrogen peroxide and 0.03% EDTAin water removes tungsten nitride at approximately 2040 Å/min. andtitanium nitride at approximately 200 Å/min. This wet etch furtherremoves tungsten oxynitride at approximately 200 Å/min. Estimatesindicate that the wet etch also removes titanium oxynitride atapproximately 20 Å/min. In contrast, the wet etch removes tungstensilicide, titanium silicide, and polysilicon at lower rates such as, byway of example, at approximately 1 Å/min. The rate of etching of thetungsten oxynitride, the titanium oxynitride, the tungsten silicide, thetitanium silicide and the polysilicon however, can vary.

While the wet etch is heated to 65° C. in one embodiment, thetemperature of the wet etch may vary over a wide range. For example, incertain embodiments, the temperature of the wet etch varies fromapproximately room temperature to approximately 85° C. One of ordinaryskill in the art will recognize that the temperature of the wet etch canbe adjusted based on the composition of the etch solution and thecomposition of the extrusions 140 to be dissolved.

In the preferred embodiment, ammonium hydroxide is added to adjust thepH of the wet etch. For example, 0.02% by weight of ammonium hydroxideadjusts the pH of the wet etch to approximately 7. The pH adjustment ofthe wet etch enhances the metal nitride removal rates withoutsignificantly damaging the remainder of the wordline stack 50.

In one embodiment, a memory array 10 is soaked in the preferred wet etchfor approximately 2 minutes to remove approximately 50 nm of tungstenoxynitride extrusions 140. The length of time of cleaning can vary overa wide range. For example, in certain embodiments, the length of time ofcleaning varies from approximately 5 minutes to approximately 30minutes. Those of skill in the art will recognize that a memory array 10can be soaked in a wet etch solution for enough time to remove as muchmetal nitride and/or metal oxynitride as required.

In the example where only 10 out of 360 memory arrays constructed on awafer operated properly after processing, a second 360 memory arraywafer was constructed. With the novel wet etch, 200 of the 360 memoryarrays operated properly after wet etch cleaning. The memory array 10 isready for further processing, in a processing block 190, as may berequired.

While application of the wet etch has been described with respect toremoval of extrusions 140 in a wordline stack 50, it should beunderstood that the wet etch can be applied to a wide variety ofsemiconductor structures wherein extrusions 140 need to be removedtherefrom. Furthermore, although the foregoing invention has beendescribed in terms of certain preferred embodiments, other embodimentswill become apparent to those of ordinary skill in the art in view ofthe disclosure herein. Accordingly, the present invention is notintended to be limited by the recitation of preferred embodiments, butis intended to be defined solely by reference to the appended claims.

What is claimed is:
 1. A method of forming at least a portion of amemory having at least a side comprising selectively removing metalnitride extrusions from a side of a portion of a memory in a manner thatdoes not substantially damage a conductive layer in the portion of thememory.
 2. The method of claim 1 wherein the metal nitride extrusionscomprise tungsten nitride extrusions.
 3. The method of claim 1 whereinthe metal nitride extrusions comprise titanium nitride extrusions. 4.The method of claim 1 wherein the memory is a SDRAM.
 5. The method ofclaim 1 wherein the memory is a static memory.
 6. The method of claim 1wherein the memory is a dynamic memory.
 7. The method of claim 1 whereinthe memory is an extended data out memory.
 8. A method of forming atleast a portion of a memory having at least a side comprisingselectively removing metal nitride extrusions from a side of a portionof a memory in a manner that does not substantially damage a barrierlayer in the portion of the memory.
 9. The method of claim 8 wherein themetal nitride extrusions comprise tungsten nitride extrusions.
 10. Themethod of claim 8 wherein the metal nitride extrusions comprise titaniumnitride extrusions.
 11. The method of claim 8 wherein the memory is aSDRAM.
 12. The method of claim 8 wherein the memory is a static memory.13. The method of claim 8 wherein the memory is a dynamic memory. 14.The method of claim 8 wherein the memory is an extended data out memory.15. A method of forming a semiconductor structure having at least a sidecomprising selectively removing metal oxynitride extrusions from a sideof a semiconductor structure in a manner that does not substantiallydamage a barrier layer in the semiconductor structure.
 16. The method ofclaim 15 wherein the metal oxynitride extrusions comprise tungstenoxynitride extrusions.
 17. The method of claim 15 wherein the metaloxynitride extrusions comprise titanium oxynitride extrusions.
 18. Themethod of claim 15 wherein the metal oxynitride extrusions comprisetitanium tungsten oxynitride.
 19. A method of forming a semiconductorstructure having at least a side comprising selectively removing metalnitride extrusions from a side of a semiconductor structure in a mannerthat does not substantially damage a polysilicon layer in thesemiconductor structure.
 20. The method of claim 19 wherein the metalnitride extrusions comprise tungsten nitride extrusions.
 21. The methodof claim 19 wherein the metal nitride extrusions comprise titaniumnitride extrusions.